Technical Field
The present disclosure relates to a microelectromechanical transducer and to a method for manufacturing the microelectromechanical transducer. In particular, the present disclosure relates to a trench-based solid-body pressure or force sensor and to a manufacturing method thereof.
Description of the Related Art
As is known, integrated pressure sensors can be manufactured with micromachining techniques. These sensors typically comprise a thin membrane, or diaphragm, suspended over a cavity provided in a silicon body. Formed within the membrane are piezoresistive elements connected together to form a Wheatstone bridge. When subjected to a pressure, the membrane undergoes deformation, causing a variation of resistance of the piezoresistive elements, and thus an unbalancing of the Wheatstone bridge. As an alternative, capacitive sensors are available, where the membrane provides a first plate of a capacitor, whereas a second plate is provided by a fixed reference. During use, deflection of the membrane generates a variation of the capacitance of the capacitor, which may be detected and associated to the pressure exerted on the membrane.
However, these semiconductor sensors may not in themselves be used for measuring high pressures in so far as they typically have low full-scale values. Thus, for high-pressure applications, piezoresistors are formed at a surface of a N-type silicon body, e.g., by means of P+ implants.
Examples of manufacturing techniques and applications are provided in U.S. Pat. No. 5,773,728. According to the disclosure of U.S. Pat. No. 5,773,728, a semiconductor sensor suitable for high-pressure applications includes piezoresistors on top of strain gauges directly connected to the surface of a silicon substrate. The active region, consisting of (i) the strain gauges, (ii) the trenches between them and (iii) the piezoresistors, is exposed to the environment. The absence of a protection structure induces risks of damage or leakage on said active region, preventing a reliable use of the sensor in harsh environments.
It is known to the present applicant that a gel may be used to protect the active region. However, the protective gel could be damaged or removed in conditions of high temperature and/or high pressure, or when in contact with specific fluids for hydrostatic pressure applications. Moreover, said protective gel would fill trenches in active regions, affecting their behavior.